. police say the ammunition, gear and fourweaponsusedinthe attack including an assault rifle, are believed to have been purchased legally. the suspect apparently received up to 50 packages in the mail in the four months leading up to the attack. he purchased 6,000 rounds of ammunition over the internet. one law enforcement official says the massacre could have been far worse if the shooter's semiautomatic rifle hadn't jammed as investigators believe it had. new york city mayor michael bloomberg yesterday called on the two presidential candidates to lead a national debate on gun control. >> somebody's got to do something about this and this requires, particularly in a presidential year, the candidates for president of the united states to stand up and once and for all say, yes, they feel terrible, yes, it's a tragedy, yes, we have great sympathy for the families but it's time for this country to do something. that's the job of the president of the united states. and i don't know what they're going to do, but i think it's incumbent on them to tell us specifically, not just in b